I think it's a responsibility for us to be a polite person.First,we are not allowed to smoke in public places.Smoking isn't only bad for our health but also has a bad smell.Besides,we shouldn't spit everywhere.It make the environment dirty and easily spread disease.What's more ,we shoud protect public property.No doubt,damaging public property is wrong behavour.All in all,we must try our best not to some impolite behaviour.